There's not a lot of information in your post. For example, do you have a P0300 (a general misfire, all cylinders) or only a single cylinder misfire, such as  P0301, P0302, P0303 or P0304? That information which matters, diagnostically, is missing. 

If there's a general misfire, whatever is going wrong is affecting all of the cylinders and the cause has to be investigated, in terms of inputs into the engine. Dirty throttle body? Dirty Mass Air Flow sensor? Unmetered air from the intake manifold? Perhaps the PCV valve is not functioning correctly? Even a dirty engine air filter can cause such problems. 

If it's only a specific misfire, then it's time to look at the plugs, the ignition coil, and the cylinder compression, and perhaps even the connectors to-and-from the electrical harness to the ignition coils. 

So, no one can give you any kind of rational answer until these types of questions have been looked at, especially on a 21 year old vehicle.